Entropy is also of great interest because it controls ICM global properties and records the thermal history of a cluster, since it is conserved in adiabatic processes. Entropy is therefore a useful quantity for studying the effects of feedback on the cluster environment and investigating any breakdown of cluster self-similarity. Most of the studies cited for the discussion of the mass profiles were also able to compute an entropy profile. Again, since only individual systems were studied, the results are somewhat controversial and it is not trivial to generalise the conclusions to the entire FG category. In particular, [1]} found that the entropy profiles out to \(R_{500}\)  of their two FGs show a considerable excess above the expectations from non-radiative simulations, especially for RXC J0216.7-4749. This is expected if significant non-gravitational processes affect the ICM. [2]} found and entropy profile that is in agreement with simulations out to \(\sim 0.9 \,R_{200}\)  and then flattens in the outskirts, due to gas clumpiness and outward redistribution. [3]} studied RXJ 1159+5531 combining Suzaku, Chandra, and XMM observations to find no evidence of the flattening in the entropy profile outside \(\sim \)  R\(_{500}\) . A similar results was also found in [4]} for the same cluster: its entropy profile is consistent with predictions from gravity-only simulations.
